1. Field of the Invention
The present invention relates to a throttle valve control apparatus of a vehicle and, more particularly, to a throttle valve control apparatus having a failure determining function of a throttle valve driving system.
2. Description of Related Art
As such a throttle valve control apparatus, for example, there is an apparatus disclosed in JP-B-64-11817. A failure of a driving circuit is detected when a drive signal to a motor built in an actuator for opening or closing a throttle valve is generated for over predetermined time period, where the magnitude of the predetermined time period, where the duration of the predetermined time period corresponds to a duration of a drive signal generated by a normally functioning system.
A control apparatus using a relay in a driving circuit of a stepping motor to drive a throttle valve has been disclosed in JP-U-63-2845.
In recent years, however, a computer has been used for control of a throttle valve. In a failure of such a computer, there is often a case where a number of drive pulses of a short time are generated. Therefore, when an elapsed time of the drive signal is merely detected as in the conventional apparatus, there is problem in that it is impossible to determine a failure when a pulse-like drive signal is generated at an abnormally high frequency.
On the other hand, even when the driving of the throttle valve is merely stopped after the occurrence of a failure was determined, the throttle valve is held at an abnormal opening degree and difficulties will occur in the subsequent operation of the vehicle.